Abstract:

Background: Identifying asymptomatic reservoirs of malaria parasites using index cases as entry points into the
community is potentially a cost-efective way towards achieving malaria elimination.
Methods: Within 1 year, 1430 confrmed malaria cases were identifed in Marani hospital, western Kenya. Fifty cases
were followed up, and 108 index case household members and 612 neighbours within a 100 m radius were screened.
As controls, samples were collected from 510 individuals matched with index cases and located at a distance of
≥500 m from them. Infections were diagnosed by microscopy and PCR while simultaneously collecting malaria vec‑
tors indoor using pyrethrum spray catches.
Results: In the index case and neighbour households, the prevalence of infection was approximately twice as high
as in control households (by PCR: index cases households: 28.9%, neighbours: 25.3%, matched controls: 12.9%).
In index case households, the indoor vector density (Anopheles gambiae and Anopheles funestus) was higher (0.46
female/house/night) than in neighbouring (0.31 f/h/n) and control houses (0.29 f/h/n).
Conclusions: Screening index case households and neighbours approximately doubles the chance to detect
asymptomatic infections compared to randomly selected households. However, even if all cases were followed up,
only a small proportion (˂ 10%) of the asymptomatic reservoir in the population would have been identifed. Control
programmes need to weigh the increased chance to fnd cases around index cases vs. the logistical challenges to
target this subgroup within the population.